Image transfer system and liquid toner for use therewith

ABSTRACT

A printing method comprising: forming a first image utilizing a liquid toner comprising carrier liquid and pigmented polymer particles having a first color; transferring the first image to an intermediate transfer member, forming at least one additional image utilizing a liquid toner comprising at least one carrier liquid and pigmented polymer particles having a second color, different from the first color, transferring the at least one additional image to the intermediate transfer member overlaid on the first image, to form a composite image on the intermediate transfer member; and further transferring the composite image to a further substrate, wherein said polymer particles in said first liquid toner and in at least one of said additional liquid toners have different compositions, aside from colorants, the differences in composition including at least one of different polymers or blends of polymers, different amounts or types of plasticizers, different amounts of solvated liquid and different compositions of solvated liquid.

The present application is a U.S. national application of PCTApplication No. PCT/IL02100090, filed on Jan. 31, 2002.

FIELD OF THE INVENTION

The present invention is related to the field of liquid toner printingsystems and in particular to multicolor printing systems.

BACKGROUND OF THE INVENTION

Liquid toner printing systems are well known. Some of such systems,utilize an intermediate transfer member. The intermediate transfermember receives a developed liquid toner image from an image formingmember (“first transfer”), such as a photoreceptor, and transfers theimage to a final substrate (second transfer). Such systems aredesignated herein as “liquid toner offset printing systems.” As usedherein, the term printer includes copiers or other machines in which thefinal product is a printed image on a substrate.

Two methodologies are used when multi-color images are to be printed.Both require the generation of multiple separations (i.e., single colorpartial images) that, when superimposed, result in the desired printedimage. Each of said images is separately generated on the image formingmember, transferred to the intermediate transfer member and transferredtherefrom to the final substrate. In some systems, the images areseparately transferred to the final substrate. In these systems, theimages are separate on the intermediate transfer member and aresuperimposed, in registration, on the final substrate. In other systems,referred to herein as “one-shot” systems, the images are separatelyformed on the image forming member and are transferred to theintermediate transfer member in registration and superposition thereon.The superposed images are transferred together to the final substrate.

In some one shot systems, a same image forming member is used togenerate the separations sequentially. In other systems a plurality ofimage forming systems are present, each of which generates an image of adifferent color, the plurality of images being superimposed on theintermediate transfer member.

Toner systems for printing liquid toner images are also well known andhave a long history. In modern liquid toner printing, the toner is basedon a composition that includes a carrier liquid and (generally charged)colored (generally pigmented) polymer based toner particles. Exemplaryexamples of such toners are described in U.S. Pat. Nos. 6,155,457;6,146,803; 5,972,548; 5,923,929; 5,554,476; 5,426,491; 5,407,771;5,346,796; 5,286,593; 5,264,313; 5,266,435; 5,231,454; 5,208,130;5,108,866; 5,048,762; 5,047,306; 4,966,824; 4,794,651; 4,794,651; 4,756,986; 4,719,026; 4,582,774; PCT publications WO 96/31808; WO 99/45433; WO96/13760; WO 01/53895 and WO 01/88619, the disclosures of all of whichare incorporated herein by reference.

In general, the various differently colored toners in a set of tonersused to print a given image have a same basic structure, namely, thatthe polymer used as the basis for the toner particles is the same forthe entire set.

SUMMARY OF INVENTION

In general, in one-shot printing, the first partial image (separation)transferred to an image transfer member remains on the image transfermember for a longer time than do the separations that are transferredlater. Since in most systems, the intermediate transfer member isheated, significantly more of the carrier liquid within the earliertransferred separations is evaporated before second transfer. Thischanges the rheology, tackiness and cohesiveness of the image and, insome cases may result in poor second transfer of some or all of theseparations and/or in different amounts and quality of transfer for thedifferent separations. This phenomenon may or may not occur, dependingon the particular polymer used, the dwell time of the separations on theintermediate transfer member, the composition of the carrier liquid, thetemperature of the intermediate transfer member and other factors. Sincethe rheology of the toner is partially dependent on the pigments used,this phenomenon may also depend on the pigments used and, for a givenset of toners, on the order of printing of the separations.

In an aspect of some embodiments of the invention, a method is providedfor design and manufacture of sets of toner of colors suitable forprinting full color images.

In some embodiments of the invention, a set of liquid toners isprovided, in which the toner properties are adjusted to reduce theeffects of differing dwell times (on the intermediate transfer member)on the physical properties of the various toner image separations.

In an embodiment of the invention, the properties, for example thosedescribed herein as effecting transfer of liquid toner separations, ofvarious toner materials, under conditions of dwell on an intermediatetransfer member, are determined or estimated. Based on thisdetermination or on experimental results, the properties of one or moreof the various toners in a set of colored toners are adjusted to improvethe second transfer of the separations. In some embodiments of theinvention, the spread in such properties caused by unequal dwell timesfor the separations or by the effects of different pigments or pigmentloadings used in the various toners is compensated for such that thetoners have a smaller spread of properties on second transfer. Such asmaller spread in properties will generally lead to a wider operatingwindow.

A general aspect of some embodiments of the invention is concerned withthe use of toners having different characteristics (other than color),for example, rheology, tackiness and/or cohesiveness, for at least someof the different colored liquid toners used in a set of liquid toners.In some embodiments, different polymers for at least some of thedifferent colored liquid toners used. In others, different carrierliquids are use. In yet others, plasticizers (additional to the carrierliquid), added to some of the colored toners and not to others or areused in different amounts in different ones of the toners. Additionally,in some of the embodiments of the invention a different plasticizingliquid is used in producing plasticized polymer which forms the basefrom which the toner particles is formed.

In an exemplary embodiment of the invention, different polymers ordifferent blend ratios of polymers are used as the basis for the pigmentparticles in at least some of the liquid toner that make up a set oftoners for printing. In general, a set of toners is made up of cyan,magenta and yellow, with optional black, orange, violet and/or greentoners. While only the first three colors are generally required, richerand or deeper colors and blacks may be possible if more colors are used.

In many of the liquid toners used today, the toner particles are formedby grinding a polymer that has been plasticized with a liquid, such as aliquid hydrocarbon, that is solvated by the polymer. In some embodimentsof the invention the liquid used to pre-plasticize the polymer isdifferent from that used as the carrier liquid for the liquid toner. Theamount of the liquid that is absorbed by the polymer is believed to playa role in the ability of the earlier produced images to undergo goodsecond transfer. In particular, the present inventors have found thatpolymers which solvate a greater amount of liquid apparently also holdliquid longer to a greater degree. Such toner polymers are thus suitablefor use as polymers for earlier transferred separations.

In some embodiments of the invention, only a portion of the polymer,which forms the basis for the later separations, is replaced by thepolymer having the higher carrier liquid holding capacity. The presentinventors have found that that it is sufficient, in some embodiments,for only a portion of the polymer to be replaced. At feast some of thepolymers having the higher holding capacity for carrier liquid also havea higher melt index than at least some of the polymer used in the pastas standard materials. In general, materials with a higher melt indexhave a higher gloss.

In some embodiments of the invention, the liquid toner in the earlierprinted separation or separations have a different chemistry than thosein the later printed separations. In some embodiments, the differentchemistry comprises a different chemistry of the toner particles withrespect to the carrier liquid.

Alternatively or additionally, the first transferred layers utilize apolymer to which a rheology (or other relevant property) adjustingadditive, such as a plasticizer, has been added. Such an additive mayreduce the viscosity of the toner to a sufficient degree that the tonerhas an acceptable rheology even with less solvated carrier liquid.

There is thus provided, in accordance with an exemplary embodiment ofthe invention, a printing method comprising:

-   -   forming a first image utilizing a liquid toner comprising        carrier liquid and pigmented polymer particles having a first        color;    -   transferring the first image to an intermediate transfer member;    -   forming at least one additional image utilizing a liquid toner        comprising at least one carrier liquid and pigmented polymer        particles having a second color, different from the first color;    -   transferring the at least one additional image to the        intermediate transfer member overlaid on the first image, to        form a composite image on the intermediate transfer member; and    -   further transferring the composite image to a further substrate,    -   wherein said polymer particles in said first liquid toner and in        at least one of said additional liquid toners have different        compositions, aside from colorants, the differences in        composition including at least one of different polymers or        blends of polymers, different amounts or types of plasticizers,        different amounts of solvated liquid and different compositions        of solvated liquid.

In an embodiment of the invention, a substantially larger portion of thecarrier liquid in said first toner image and in said at least oneadditional toner image are evaporated while said respective images areon the intermediate transfer member, said evaporation changing one ormore of the rheology, tackiness or cohesiveness characteristics of therespective image, such that said one or more characteristic issubstantially more similar when said images are further transferred fromthe intermediate transfer member than when they are transferred to theintermediate transfer member.

In an embodiment of the invention, the carrier liquid is a liquidhydrocarbon. In an embodiment of the invention, the solvated liquid is aliquid hydrocarbon. Optionally, the carrier liquid is the same as thesolvated liquid. Alternatively, the carrier liquid is not the same asthe solvated liquid.

In an embodiment of the invention, the intermediate transfer member isat an elevated temperature and wherein said first and at least oneadditional liquid toners in said images, as transferred to theintermediate transfer member, have different characteristics oftackiness, rheology or cohesiveness at said elevated temperature.

Optionally, the first and at least one additional liquid toners havesubstantially similar characteristics at 25° C.

Optionally, the polymer particles pigmented polymer particles solvatesaid carrier liquid in said first and at least one additional liquidtoner at said elevated temperature.

In an embodiment of the invention, at least said first liquid tonercomprises a plasticizer for said toner particles, said plasticizer beingadditional to or different from in amount or type from any plasticizerthat may be present in said at least one additional liquid toner.Optionally, the plasticizer comprises one or more of Di Butyl phtalate ,Acetyl tri-ethyl citrate or Acetyl tri-butyl citrate.

In an embodiment of the invention, the polymer particles in said firstliquid toner comprise a different polymer or mixture of polymers than dothe polymer particles in said at least one additional toner. Optionally,the polymers in the particles of the different toners are different.Alternatively or additionally, the polymers are different in that thepolymer of one of the particles is formed of a mixture of polymers saidmixture comprising a polymer comprised in the other particles and atleast one additional polymer not comprised in the one particle.Alternatively or additionally, the polymers are different in that thepolymer of the particles are formed of a mixture of polymers theproportion of polymers in said mixture being different for therespective particles. Optionally, one of the polymers is an ethyleneacid/methacrylic acid copolymer. Alternatively or additionally, one ofthe polymers is an Acid-Modified Ethylene Acrylate. Alternatively oradditionally, one of the polymers is an ethylene acrylic acid copolymer.

In an embodiment of the invention, the polymer particles are formed in aprocess in which the polymer of the particles is heated with andplasticized by a liquid, some of which remains solvated by the polymerafter cooling the particles and wherein the proportionate amount orcomposition of said remaining solvated liquid is different for theparticles in the first and at least one additional toner. Optionally,the proportionate amount is different. Optionally, the proportion byweight of liquid in the first toner particles is over 30% or 35% byweight of polymer. Optionally, the proportion by weight of liquid in thetoner particles of at least one additional toner is less than 30% or 25%by weight of polymer. Optionally, the composition of the remainingsolvated liquid is different.

Optionally, the liquid solvated in the toner particles of the firsttoner comprises liquid having an evaporation time compared toDiethylether of more than 150.

Optionally, the liquid solvated in the toner particles of at least oneadditional toner comprises liquid having an evaporation time compared toDiethylether or greater than 250.

Optionally, the ratio of evaporation rates of the liquids solvated inthe first and second toner particles is at least 2:1, 3:1 or 4:1.

In an embodiment of the invention, the carrier liquid used in said firstand at least one additional toner is different or comprises a mixture ofdifferent carrier liquids or a mixture of the same carrier liquids indifferent proportions.

In an embodiment of the invention, the toner particles are charged.

In an embodiment of the invention, forming an image comprises:

-   -   forming a latent electrostatic image on an image forming        surface;    -   contacting the image with a liquid toner to form a visible        image.

Optionally, the liquid toners comprise at least cyan, magenta and yellowtoners. Optionally, the liquid toners comprise a black toner.Optionally, the liquid toners comprise one or more of violet, orange andgreen toners.

There is further provided, in accordance with an exemplary embodiment ofthe invention a set of at least two liquid toners for printingmulti-color images, each said toner having a different color, each saidtoner comprising:

-   -   a carrier liquid,    -   toner particles comprising a pigmented polymer of a given color,        different from the color of pigmented particles in other toners        in the set,    -   wherein said polymer particles in a first liquid toner of said        set and in at least one of the other liquid toners have        different compositions, aside from colorants, the differences in        composition including at least one of different polymers or        blends of polymers, different amounts or types of plasticizers,        different amounts of solvated liquid and different compositions        of solvated liquid.

In an embodiment of the invention, the carrier liquid is a liquidhydrocarbon. In an embodiment of the invention, the solvated liquid is aliquid hydrocarbon. Optionally, the carrier liquid is the same as thesolvated liquid. Alternatively, the carrier liquid is not the same asthe solvated liquid.

In an embodiment of the invention, the first and at least one additionalliquid toners have substantially similar characteristics at 250° C.

Optionally, the polymer particles pigmented polymer particles solvatesaid carrier liquid in said first and at least one additional liquidtoner at 75° C.

In an embodiment of the invention, at least said first liquid tonercomprises a plasticizer for said toner particles, said plasticizer beingadditional to or different from in amount or type from any plasticizerthat may be present in said at least one additional liquid toner.Optionally, the plasticizer comprises one or more of Di Butyl phtalate,Acetyl tri-ethyl citrate and Acetyl tri-butyl citrate.

In an embodiment of the invention, the polymer particles in said firstliquid toner comprise a different polymer or mixture of polymers than dothe polymer particles in said at least one additional toner. Optionally,the polymers are different. Optionally, the polymers are different inthat the polymer of one of the particles is formed of a mixture ofpolymers said mixture comprising a polymer comprised in the otherparticles and at least one additional polymer not comprised in the oneparticle. Optionally, the polymers are different in that the polymer ofthe particles are formed of a mixture of polymers the proportion ofpolymers in said mixture being different for the respective particles.Optionally, one of the polymers is an ethylene acid/methacrylic acidcopolymer. Optionally, one of the polymers is an Acid-Modified EthyleneAcrylate. Optionally, one of the polymers is an ethylene acrylic acidcopolymer.

In an embodiment of the invention, the polymer particles are formed in aprocess in which the polymer of the particles is heated with andplasticized by a liquid, some of which remains solvated by the polymerafter cooling the particles and wherein the proportionate amount orcomposition of said remaining solvated liquid is different for theparticles in the first and at least one additional toner. Optionally,the proportionate amount is different. Optionally, the proportion byweight of liquid in the first toner particles is over 30% or 35% byweight of polymer. Optionally, the proportion by weight of liquid in thetoner particles of at least one additional toner is less than 30% or 25%by weight of polymer. Optionally, the composition is different.

In an embodiment of the invention, the liquid solvated in the tonerparticles of the first toner comprises liquid having an evaporation timecompared to Diethylether of more than 150 or 250. Optionally, the liquidsolvated in the toner particles of at least one additional tonercomprises liquid having an evaporation time compared to Diethylether ofless than 150.

In an embodiment of the invention, the ratio of evaporation times of theliquids solvated in the first and second toner particles is at least2:1, 3:1 or 4:1.

In an embodiment of the invention, the carrier liquid used in said firstand at least one additional toner is different or comprises a mixture ofdifferent carrier liquids or a mixture of the same carrier liquids indifferent proportions.

In an embodiment of the invention, the toner particles in said first andat least one other liquid toners have different characteristicsincluding at least one of rheology, tackiness and cohesiveness, for atleast some of the different colored liquid toners in the set of liquidtoners. Optionally, said toners have said different characteristics atelevated temperatures.

Optionally, the polymer particles solvate said carrier liquid atelevated temperatures, suitable for fusing and fixing the toner to asubstrate. Optionally, a first liquid toner at a first, higher solidsconcentration has substantially the same characteristic as anotherliquid toner of the set at a second lower solids concentration at anelevated temperature at which the toner particles solvate the carrierliquid.

In an embodiment of the invention, the carrier liquid is different forat least two liquid toners of the set of liquid toners. Optionally, thecarrier liquid in a first member of the set comprises a first carrierliquid component not present in at least one other liquid toner of theset, said first carrier liquid component having a slower evaporation athigh temperatures than carrier liquid components present in both liquidtoners. Optionally, the carrier liquid in a first member of the setcomprises a first carrier liquid component present in at least one otherliquid toner of the set in a higher proportion than in at least oneother liquid toner of the set, said first carrier liquid componenthaving a slower evaporation at high temperatures than other carrierliquid components present in both liquid toners.

In an embodiment of the invention, the liquid toners comprise at leastcyan, magenta and yellow toners. Optionally, the liquid toners comprisea black toner. Optionally, the liquid toners comprise one or more ofviolet, orange and green toners.

There is further provided, in accordance with an exemplary embodiment ofthe invention, a method of producing at least two members of a set ofdifferently colored liquid toners comprising:

-   -   for each of the members, heating a polymer material with a        hydrocarbon liquid by which the polymer material is plasticized;        and    -   forming pigmented toner particles, based on the plasticized        polymer material for each of the toners,    -   wherein some of the hydrocarbon liquid remains solvated by the        polymer after cooling the particles and wherein the        proportionate amount or composition of said remaining solvated        hydrocarbon liquid is different for the particles in the at        least two members of the set.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary, non-limiting, embodiments of the invention are described withreference to the appended drawings, in which:

FIG. 1 shows a methodology for the design and production of toners forone shot printing with reduced variation at second transfer; and

FIGS. 2 and 3 show a simplified schematic exposition of an exemplaryone-shot printing system in accordance with an exemplary embodiment ofthe invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a simplified flow chart 210, for the design and adjustmentof a set of toners for use in a one shot printing system, in accordancewith an exemplary embodiment of the invention.

At 212 an estimate is made of the changes in the rheology of the toneras a function of dwell time. This estimate is a function of the type ofpolymer or polymer blend used as the basis for the toner particles. Itis also a function of the temperature of the intermediate transfermember and of the type of carrier liquid used in the toner. It is also afunction of the liquid used to solvate the polymer. Finally, it is afunction of additives that are added to the toner particles that adjustthe rheology of the toner at second transfer.

The starting point for the process is often a toner that has good secondtransfer for a given dwell time, intermediate transfer membertemperature and other operating conditions of the printer. The exactphysical properties of the toner material need not be known, however, inan embodiment of the invention, the properties of the other toners areadjusted to provide similar properties. It is useful to consider thetoner having the lowest dwell time as having the “goal” properties,although the toner used for other separations can be used to define thegoal.

Thus, at 214 a first adjustment for one or more of the other toners isdetermined. Any of the methodologies described below may be used tocompensate for the increased dwell time of the other (than the “goal”)toners.

At 216, a first iteration for a set of toners is determined. In manycases, this iteration, based on a very general knowledge of the effectsof various changes in the composition of the toner will give an improvedset of toners that need not be further adjusted.

At 218, the set of toners is optionally tested by printing testseparations. The quality of the images is determined, for example, bymeasurement and other tests such as adhesion, known in the art. In anembodiment of the invention, the printer characteristics are varied todetermine the operating window of the set of toners. For example thetemperature of the intermediate transfer member and/or the first and/orsecond transfer pressure, and/or the first transfer voltage and/ordevelopment parameters are used to determine the size of the operatingwindow.

A second, optional, iteration 220 and a second set of tests 222 may beperformed in which those toners that restrict the operating window arefurther adjusted and tested, in accordance with the changes in the tonercharacteristics that are described below. In general, a major cause ofvariation in second transfer between the separations is the amount ofliquid remaining in (and solvating) the image. Methods for adjustingthis amount of liquid by changing the polymers (and blends) used,changing the liquid used to solvate the polymer in the formation of thetoner and adding plasticizer, are described below. Other characteristicsthat may effect the transfer may be adjusted similarly. Furtheriterations may also be performed.

In order to speed up the convergence of the iterative process, tests maybe made to characterize the toner properties under conditions of varieddwell as a function of the below-described adjustments in the toner.While such iteration is desirable, it is not necessary for achievingimproved results, based on present knowledge of the functions andeffects of the variations of the toner constitution described herein.However, such iteration may be required to produce optimal toner sets.

FIGS. 2 and 3 show a simplified schematic exposition of an exemplaryone-shot printing system 11, in accordance with an embodiment of theinvention. For convenience, the apparatus of FIGS. 2 and 3 is verysimplified and does not include many of the details present in suchapparatus, since the liquid toners of the invention are useful for awide variety of designs for existing printers and since these existingdevices need little or no substantive redesign. For details of somesystems for which the invention is useful, the reader is referred to theextensive patent literature on the subject of liquid toner printingsystems and especially to the patents and applications originallyassigned to Indigo, N.V. and its predecessor Spectrum Sciences B.V. Ingeneral, the printing system is similar to that described in U.S. Pat.No. 5,915,152, the disclosure of which is incorporated herein byreference, since this publication describes, generally, an apparatuscurrently used for printing. However, as indicated above, otherapparatus for producing toner images may be used, since, in general, thepresent invention is not specific to the method of forming the tonerimage before transfer to an intermediate transfer member.

As seen in FIGS. 2 and 3 system 11 comprises an imaging sheet, typicallyan organic photoreceptor 12, typically mounted on a rotating drum 10.Drum 10 is rotated about its axis by a motor or the like (not shown), inthe direction of arrow 18, past a charging apparatus 14, preferably acorotron, scorotron or roller charger or other suitable chargingapparatus as are known in the art and which is adapted to charge thesurface of sheet photoreceptor 12. The image to be reproduced is focusedby an imager 16 upon the charged photoreceptor 12 at least partiallydischarging the photoconductor in the areas struck by light, therebyforming the electrostatic latent image. Thus, the latent image normallyincludes image areas at a first electrical potential and backgroundareas at another electrical potential.

Photoreceptor sheet 12 may use any suitable arrangement of layers ofmaterials as is known in the art, however, as described and referencedin U.S. Pat. No. 5,915,152, certain of the layers are optionally removedfrom the ends of the sheet to facilitate its mounting on drum 10.Alternatively, photoreceptor 12 may be deposited on the drum 10 and mayform a continuous surface. Furthermore, photoreceptor 12 may be anon-organic type photoconductor based, for example, on a compound ofSelenium.

It should be noted that in other, alternative, embodiments of theinvention, non-electrophotographic methods may be used for generatingthe electrostatic latent image. For example, the latent image may be achangeable or a permanent latent image generated by ionographic or otherelectrostatic image forming means or other methods for forming latentimages, as known in the art, may be used.

In a exemplary embodiment of the present invention, imaging apparatus 16is a modulated laser beam scanning apparatus, or other laser imagingapparatus such as is known in the art.

Also associated with drum 10 and photoreceptor sheet 12, in theexemplary embodiment, are a multicolor toner curtain applicator 20, adeveloping assembly 22, color specific cleaning blade assemblies 34, abackground cleaning station 24, an electrified squeegee 26, a backgrounddischarge device 28, an intermediate transfer member 30, cleaningapparatus 32, and, optionally, a neutralizing lamp assembly 36. Some ofthese elements may be omitted or replaced by elements with similarfunctions, in some embodiments of the invention.

In the described embodiment, developing assembly 22 includes adevelopment roller 38. Development roller 38 is generally spaced fromphotoreceptor 12 thereby forming a gap therebetween of typically 40 to150 micrometers and is charged to an electrical potential intermediatethat of the image and background areas of the image. Development roller38 is thus operative, when maintained at a suitable voltage, to apply anelectric field to aid development of the latent electrostatic image.

Development roller 38 typically rotates in the same sense as drum 10 asindicated by arrow 40. This rotation provides for the surface of sheet12 and development roller 38 to have opposite velocities at the gapbetween them.

A multicolor toner curtain applicator 20, whose operation and structureis described in U.S. Pat. No. 5,915,152, is preferably fixedly mountedjuxtaposed with a portion of the surface of photoreceptor 12,hereinafter referred to as an application region, upstream of adevelopment region 44 between photoreceptor 12 and development roller38. In accordance with the described embodiment, applicator 20 producesa continuous body of liquid toner, hereinafter referred to as a tonercurtain, which propagates in the direction of the application region.For color imaging, a plurality of different color toner curtains aresequentially applied to the application region by toner applicator 20.

Optional color specific cleaning blade assemblies 34, as known in theart, are operatively associated with developer roller 38 for separateremoval of residual amounts of each colored toner remaining thereonafter development. Each of blade assemblies 34 is selectably broughtinto operative association with developer roller 38 when toner of acolor corresponding thereto is supplied to the application region bytoner curtain applicator 20. The construction and operation of cleaningblade assemblies is described in PCT Publication WO 90/14619 and in U.S.Pat. No. 5,289,238, the disclosures of which are incorporated herein byreference.

Each cleaning blade assembly 34 includes a toner directing member 52which serves to direct the toner removed by the cleaning bladeassemblies 34 from the developer roller 38 to separate collectioncontainers 54, 56, 58, 60, 154 and 156, one for each color toner, toprevent contamination of the various color toners by mixingtherebetween. The different color toners collected by collectioncontainers 54, 56, 58, 60, 154 and 156 are recycled to correspondingtoner reservoirs 55, 57, 59, 61, 155 and 157. An optional final tonerdirecting member 62 optionally always engages the developer roller 38and the toner collected thereat is supplied into collection container 64and thereafter to a carrier-liquid reservoir 65 via a separator 66 whichis operative to separate relatively clean carrier liquid from thevarious colored toner particles. The separator 66 may be typically ofthe type described in U.S. Pat. No. 4,985,732, the disclosure of whichis incorporated herein by reference.

In some embodiments of the invention, as described in PCT Publication WO92/13297, the disclosure of which is incorporated herein by reference,where the imaging speed is very high, a background cleaning station 24,typically including a reverse roller 46 and a wetting roller 48, isoptionally provided. Reverse roller 46 which rotates in a directionindicated by arrow 50 is preferably electrically biased to a potentialintermediate that of the image and background areas of photoconductivedrum 10, but different from that of the development roller. Reverseroller 46 is preferably spaced apart from photoreceptor sheet 12 therebyforming a gap therebetween which is typically 40 to 150 micrometers.

Wetting roller 48 is preferably partly immersed in a fluid bath 47,which preferably contains carrier liquid received from carrier liquidreservoir 65 via conduit 88. Wetting roller 48, which preferably rotatesin the same sense as that of drum 10 and reverse roller 46, operates towet photoreceptor sheet 12 with non-pigmented carrier liquid upstream ofreverse roller 46. The liquid supplied by wetting roller 48 replaces theliquid removed from drum 10 by development assembly 22, thus allowingthe reverse roller 46 to remove charged pigmented toner particles byelectrophoresis from the background areas of the latent image. Excessfluid is removed from reverse roller 46 by a liquid directing member 70which continuously engages reverse roller 46 to collect excess liquidcontaining toner particles of various colors which is in turn suppliedto reservoir 65 via collection container 64 and separator 66.

Details of the operation of roller 46 and wetting roller 48 aredescribed, in more detail, in U.S. Pat. No. 5,915,152. It should beunderstood that the apparatus shown in FIGS. 2 and 3 are not, per senew. Rather, the apparatus shown in FIGS. 2 and 3 is described as anexample of an apparatus that can be used with the toners of theinvention.

The apparatus embodied in reference numerals 46, 47, 48 and 70 isgenerally not required for low speed systems, but is preferably includedin high speed systems.

Optionally, an electrically biased squeegee roller 26 is urged againstthe surface of sheet 12 and is operative to remove liquid carrier fromthe background regions and to compact the image and remove liquidcarrier therefrom in the image regions. Squeegee roller 26 is preferablyformed of resilient slightly conductive polymeric material as is wellknown in the art, and is optionally charged to a potential of severalhundred to a few thousand volts with the same polarity as the polarityof the charge on the toner particles.

Discharge device 28 is operative to flood sheet 12 with light whichdischarges the voltage remaining on sheet 12, mainly to reduceelectrical breakdown and improve transfer of the image to intermediatetransfer member 30. Operation of such a device in a write black systemis described in U.S. Pat. No. 5,280,326, the disclosure of which isincorporated herein by reference.

FIGS. 2 and 3 further show that multicolor toner curtain applicator 20receives separate supplies of colored toner typically from the sixdifferent reservoirs 55, 57, 59, 61, 155 and 157. FIG. 1 shows the sixdifferent colored toner reservoirs 55, 57, 59, 61, 155 and 157, one ofwhich typically contains a black toner, denoted K. The other reservoirsmay contain any suitable standard or custom-selected colors, for exampleYellow, Magenta and Cyan denoted Y, M and C, respectively, and other,special, colors denoted S₁ and S₂, respectively. Pumps 90, 92, 94, 96,190 and 192 may be provided along respective supply conduits 170, 172,174, 176, 180 and 182 for providing a desired amount of pressure to feedthe colored toner to multicolor toner applicator 20. The use of sixdifferent reservoirs allows for custom colored tones in addition to thestandard process colors. Alternatively, for standard 4-color imaging,toner applicator 20 is associated with only four different color tonerreservoirs, typically containing the colors Yellow, Magenta, Cyan andBlack.

Intermediate transfer member (ITM) 30 may be any suitable intermediatetransfer member, for example, as described in U.S. Pat. Nos. 4,684,238and 4,974,027 or in PCT Publication WO 90/04216, the disclosures ofwhich are incorporated herein by reference. Alternatively, ITM 30 has amultilayered transfer portion such as those described below or in U.S.Pat. Nos. 6,070,042; 5,754,931; 5,745,829; 5,592,269; 5,497,222;5,335,054; 5,262,829; 5,089,856, 5,047,808, the disclosures of all ofwhich are incorporated herein by reference. Member 30 is maintained at asuitable voltage and temperature for electrostatic transfer of the imagethereto from the image bearing surface of photoreceptor 12. Intermediatetransfer member 30 is preferably associated with a pressure roller 71for transfer of the image onto a final substrate 72, such as paper,preferably by heat and pressure.

Cleaning apparatus 32 is operative to scrub clean the surface ofphotoreceptor 12 and preferably includes a cleaning roller 74, a sprayer76 for spraying a non polar cleaning liquid, preferably chilled carrierliquid from reservoir 65, and a wiper blade 78 to complete the cleaningof the photoconductive surface. The sprayed carrier liquid assists inthe scrubbing process and cools the photoreceptor surface. Cleaningroller 74 which may be formed of any synthetic resin known in the artfor this purpose is driven in the same sense as drum 10 as indicated byarrow 80, such that the surface of the roller scrubs the surface of thephotoreceptor. Any residual charge left on the surface of photoreceptorsheet 12 may be removed by flooding the photoconductive surface withlight from optional neutralizing lamp assembly 36, which may not berequired in practice.

In accordance with exemplary embodiments of the invention, afterdeveloping each image in a given color, the single color image istransferred to intermediate transfer member 30. Subsequent images indifferent colors are sequentially transferred in alignment with theprevious image onto intermediate transfer member 30. When all of thedesired images have been transferred thereto, the complete multi-colorimage is transferred from transfer member 30 to substrate 72. Impressionroller 71 only produces operative engagement between intermediatetransfer member 30 and substrate 72 when transfer of the composite imageto substrate 72 takes place.

In relevant embodiments of the invention, the toner used is a liquidtoner comprising toner particles based on a polymer and having a carrierliquid that is solvated by the polymer at elevated temperatures.

A characteristic time for the above process is the “cycle time”. This isthe time that it takes the intermediate transfer member to make acomplete rotation. Based on this time, the first layer transferred tothe intermediate transfer member is on the heated intermediate transfermember for n-1 cycles, where n is the number of separations printed.Each subsequent separation is on the intermediate transfer member for 1less cycle. In addition, each separation is typically on theintermediate transfer member for about an additional ¼-¾ of a cycle,depending on the relative position of first and second transfer aroundthe intermediate transfer member. Thus, there is a difference of betweenn-¼ and n-¾ cycle times for dwell times of the first and lastseparations. For a process in which the impression rate is 8,000/hourthe cycle time is about ½ second. Thus, for a multi-separation print,the first separation may be on the heated intermediate transfer memberfor several seconds. This time is long enough for there to be enoughevaporation to cause substantial changes in the rheology (and/or otherrelevant properties of the toner particles in the separation.

Thus, for the same basic combination of polymer and carrier liquid, therheology may change enough during the time that the first separation ison the intermediate transfer member, to bring its rheology out of adesirable range. On the other hand, if the toner (of the prior art) isconstituted so that the first layer has a proper rheology after its longdwell, then the last layer (which is on the intermediate transfer memberonly a short time) may be out of the range of usable rheologies.

The phenomena of different rheologies of different toners is alreadyknown to the inventors. For example, standard toner utilizing carbonblack as a pigment for black toner particles dries faster than otherpigmented toners. Thus, in a one shot system utilizing black toner, theblack separation is usually transferred last to the intermediatetransfer member.

The solvation properties of polymers vary. Many polymers do not solvatethe carrier liquid at all. Other polymers may give up their liquidrelatively easily when heated, while others will retain the solvatedliquid (and thus remain plasticized and/or tacky) for a longer period.Furthermore, the amount of solvation also depends on the type of liquidused.

According to one aspect of the invention, the polymer used for at leastthe first produced layer is different in constitution than that used forat least some of the subsequent layers.

In some embodiments a mixture of different polymers is used for thetoner particles of at least some of the separations. For example, thefirst and last separations may comprise a different mixture of polymers,with some of the intermediate separations having the same rheology asthe first and last separations or having intermediate rheologicalproperties.

Table 1 shows different amounts of swelling for various polymer resinswhen heated together with different mineral oils that are compatible(depending on the percentages used) with known liquid toner imagingprocesses. Swelling is defined as the percentage increase in weight of apolymer when heated together with the liquid to a temperature at whichis absorbs a large amount of the liquid and then allowed to cool to roomtemperature (25° C.). In other words, it is an indication of the amountof liquid that is “trapped” with the polymer, in the solvation process.In the following table, Bynel 2002 and 2022 (DuPont) Acid-ModifiedEthylene Acrylates, with different Melt points (ASTM Test Methods DSC,D3418) and Melt indexes (ASTM Test method D1238, 190° C./2.16 Kg). TheBynel 2002 has a melt point of 91° C. Its Melt index is about 10 dg/min.The Bynel 2022 has a melt point of 87° C. and a melt index of 35.Primacor 5990I (DOW) is an ethylene acrylic acid copolymer having a meltindex of 1300 (at 125° C.). Nucrels are ethylene acid/methacrylic acidcopolymer resins. Nucrel 699 has a Melt flow index of 100 and a meltingpoint of 94° C. Nucrel 599 has a melt flow index of 500 and a meltingpoint of 98° C. Isopar H, Isopar L and Isopar M are aliphatichydrocarbons sold by Exxon and Marcol 82 is a white mineral oil sold byExxon. The relative evaporation times of the Isopars (compared toDiethylether) are H=65, L=150 and M=680. While these numbers indicate alow evaporation rate (high evaporation time), the differences inevaporation are significant in the context of a thin image on a heatedintermediate transfer member. Marcol 82 is very stable with temperatureIt is noted that while Isopar H has in the past been used as a carrierliquid for liquid toners, it is generally not so used due to its highvolatility. Marcol 82 is used as a minor ingredient in some liquidtoners, but is not its very low volatility precludes the use of largeamounts in toners. It is further noted that some of these polymers maybe too soft to be used alone as toner polymers since they may haverelatively low abrasion resistance. Thus, the toner materials aregenerally chosen based on other considerations in addition to theconditions described herein.

TABLE 1 Polymer Solvated Liquid Swell in % W/W Bynel 2022 Isopar H 52.9Isopar L 51.8 Isopar M 47.4 Marcol 82 17.8 Bynel 2002 Isopar H 39.6Isopar L 38.6 Isopar M 37.1 Marcol 82 13.8 Primacor 5990 Isopar H 39.0Isopar L 37.1 Isopar M 34.5 Marcol 82 7.3 Nucrel 599 Isopar H 28.5Isopar L 27.6 Isopar M 21.7 Marcol 82 5.9 Nucrel 699 Isopar H 22.2Isopar L 21.7 Isopar M 21.6 Marcol 82 5.7

It is apparent that the Bynels and the Primacor resins have a highabsorption of all of the Isopars (more than 34%) and that the Nucrelshave a lower absorption of the Isopars (less than 28.5%). The presentinventors have found that when a mixture of Bynel 2002 and Nucrel 699are used as the polymer base of toner particles in a liquid toner, thesecond transfer of separations that are transferred first to theintermediate transfer member is greatly improved over the transfer forstandard toners based on Nucrel 699. The amount of Bynel 2002 that isneeded for complete transfer of the separation varies depending on alarge number of factors, for example, the pigment used, the dwell time,the number of separations, the temperature of the intermediate transfermember and the amount of liquid that is removed before first transfer.However, once the conditions are set, a near optimum set of toners canbe achieved with a reasonable amount of experimentation. The polymerused can be between 0-100% by weight for each of the materials,depending on the order of printing of the particular separation. In anembodiment of the invention, at least one of the colors has a largeproportion of Bynel 2002 (50-100%) and a second color (to be transferredto the intermediate transfer member later) has a low proportion (0-30%).Furthermore, the proportion of Bynel may be increased (or decreased) forthose colors in which the pigments affect the rheology adversely, forexample by absorbing the liquid or by otherwise increasing (ordecreasing) the hot viscosity of the toner particles on the intermediatetransfer member at second transfer. Although the above discussion iscentered on combinations of Bynel 2002 and Nucrel 699, other materials,both shown and not shown are believed to be usable instead of thesematerials, utilizing the teaching of the invention. For example, Bynel2022 gives similar results.

In particular, it is believed that utilizing different mixtures ofpolymers as the base for a set of colored toners for a one-shot transfersystem can be useful if the mixtures are chosen such that the spread inrheologic characteristics of the images formed on the intermediatetransfer member are reduced at the time of second transfer.

In accordance with an exemplary embodiment of the invention, 600 gramsof a polymer, as described below, is mixed together with 1,400 grams ofIsopar L at 130° C. in a Ross Double Planetary mixer for 1 hour at a v=2speed setting, followed by 2 hours at 130° C. at a v=5 setting. Theheating is then switched off and the material is allowed to cool whilebeing mixed at a speed setting of v=4 for 1 hour followed by continuedcooling at v=2 until the temperature reaches 30° C.

The resulting material comprises a mixture of Isopar L and polymer withsolvated Isopar that is held within the polymer material.

909.8 grams of the solvated polymer is charged, together with 85.7 gramsof Hostaperm Yellow 6GL and Novoperm Yellow 5GD70 (Clarint) and 1.035 gof aluminum stearate (a charge improvement additive), into an S-1atrittor (Union Process) filled with 3/16″ chrome steel balls. Theresulting mixture is ground for 3 hours at 55° C. followed by grindingat 17 hours at 40° C. to produce a yellow liquid toner concentratehaving a non-volatile solids content of 18%, by weight, and an averageparticle size of 7 micrometers as measured by a Coulter Particle SizeAnalyzer. Other colored toners are produced in a similar manner byreplacing the Yellow pigment by pigments having other colors, as is wellknown in the art. Additional Isopar L is added to reduce thenon-volatile solids concentration to 2% and charge director, as known inthe art is added. About 2% Marcol 82 may also be added.

In some embodiments of the invention, Nucrel 699 is used as the polymerfor at least some of the colored toners. In others a mixture of one ofthe Nucrels and Bynel 2022 or Bynel 2002 or Primacor 5990 or othermixtures including having one or more of the characteristics describedabove, is used. In some embodiments of the invention, one of thecomponents has a swell over 30% in the liquid used in the first stage ofthe processes described above and a second component has a swell ofunder 30%. Alternatively or additionally, the swell ratios should bedifferent by a factor of more than about 1.5 to 1. However, use ofhigher volatility liquids (such as Isopar H) for the first stage of theprocess may be less desirable since the Isopar H may evaporate duringthe time the image is on the intermediate transfer member.

Use of different toner polymer blends for the toner particles allows foradjusting the mounts of hydrocarbon liquid trapped in the polymer forthe different colors and allows for adjustment of the rheologicalcharacteristics of the toner images on the intermediate transfer memberto compensate for one or more of differing effects of time of the imageon the heated intermediate member (and thus difference in the amount ofliquid that is evaporated), the effects of different pigments on therheology of the toner particles. At present it is believed that bestresults (and a widest operating window) results when the rheology of thetoner images is the same for all the separations at second transfer.

Alternatively or additionally, in some embodiments of the invention, aless volatile hydrocarbon liquid is used for the preparation of thesolvated polymer than for the bulk of the carrier liquid for thosetoners that are printed first. Thus in the first stage of preparationdescribed above, the Isopar L may be replaced by Isopar M. Some of thehydrocarbon liquid in the second stage may also be Isopar M. Isopar Mhas a lower evaporation than Isopar L. Optionally, the volatility of thesolvated liquid in the first stage should be less than 4 and thevolatility of the bulk of the carrier liquid in the final liquid tonershould be more than 4. Optionally, the ratios of the volatilities shouldbe at least 1.5:1. Optionally it is more than 2 or 3:1. Optionally, itis 4:1. However, it should be understood that the amount of swellingshould be high enough so that there is substantial solvation. Generally,it is believed that the combination of liquid and polymer used in thefirst processing stage should result in swelling of at least 20%,optionally more than 25 or 30%.

A number of combinations are thus seen to be especially desirable. Forexample, Isopar L can be used with varying combinations of Bynels orPrimacor and Nucrels. The toner particles used for the first separationtransferred to the intermediate transfer member would have a relativelyhigh percentage of Bynel or Primacor (or be entirely of these materials)and the toner particles used in a later separation would have a largerpercentage of the Nucrels (or be entirely of these materials.

Alternatively, toner particles in all the separations could be made ofthe same material, such as Nucrel 699 and the first stage of manufactureof the toner for the first separation could use Isopar M and at leastone of the later separations could use Isopar L. In some embodiments thefirst transferred separation could use both a higher percentage of Bynelor Primacor and Isopar M in the first stage of manufacture and a laterseparation could be based mostly or completely on a Nucrel and Isopar L.Other combinations will occur to a person of skill in the art.

Alternatively or additionally an additional plasticizer, over an abovethe liquid hydrocarbon that is solvated by the toner polymer is used inthe formulation of some or all of the toner particles. In general, alarger amount of plasticizer is used in some of the colored toners thanin others, with the larger amounts being used in those toners that aretransferred first to the intermediate transfer member or in those tonersthat have a high viscosity for other reasons (such as black tonerspigmented with carbon black. Optionally, no plasticizer is used in oneor more of the colors in the set. Useful plasticizers are believed toinclude Di Butyl phtalate, Acetyl tri-ethyl citrate and Acetyl tri-butylcitrate. Other plasticizers may also be used.

The invention has been described in the context of a best mode forcarrying it out. It should be understood that not all the features shownin any one drawing may be present in an actual device, in accordancewith some embodiments of the invention and that some features describedwith respect to one figure may be in another embodiment as well.Furthermore, variations on the methods and apparatus shown are includedwithin the scope of the invention, which is limited only by the claims.Such variations may include use of a computer program to carry out someof the methods, the replacement of hardware by software, software byhardware and the replacement of hardware or software by firmware.

As used herein, the terms “have”, “include” and “comprise” or theirconjugates, as used herein mean “including but not limited to”.

1. A printing method for a one-shot printing system, the methodcomprising: determining a dwell condition of a first liquid toner and ofan additional liquid toner on a intermediate transfer member, whereinthe first liquid toner and the additional liquid toner are adjustedaccording to the dwell conditions; forming a first image utilizing thefirst liquid toner comprising at least one carrier liquid and pigmentedpolymer particles having a first color; transferring the first image tothe intermediate transfer member; forming at least one additional imageutilizing the additional liquid toner comprising the at least onecarrier liquid and pigmented polymer particles having a second color,different from the first color, a polymer in said pigmented particleshaving been solvated and swelled by a liquid at an elevated temperature;transferring the at least one additional image to the immediate transfermember, wherein said polymer particles in said first liquid toner and inat least one of said additional liquid toners have differentcompositions, aside from colorants, the differences in compositionincluding at least one of different polymers or blends of polymers,different amounts or types of plasticizers, different amounts ofsolvated liquid and different compositions of solvated liquid; andtransferring the first image and the at least one additional image as acomplete image from the intermediate transfer member to a substrate. 2.A method according to claim 1 wherein a portion of the carrier liquid insaid first toner image and in said at least one additional toner imageare evaporated while said respective images are on the intermediatetransfer member, said evaporation changing one or more of a rheology, atackiness or a cohesiveness characteristics of the respective image,such that said one or more characteristic is similar when said imagesare further transferred to the intermediate transfer member.
 3. A methodaccording to claim 1 wherein the at least one carrier liquid is a liquidhydrocarbon.
 4. A method according to claim 1 wherein said intermediatetransfer member is at an elevated temperature and wherein said first andat least one additional liquid toners in said images, as transferred tothe intermediate transfer member, have different characteristics oftackiness, rheology or cohesiveness at said elevated temperature.
 5. Amethod according to claim 4 wherein said first and at least oneadditional liquid toners have similar characteristics at 25 degree C. 6.A method according to claim 1 wherein said pigmented polymer particlessolvate said carrier liquid in said first and at least one additionalliquid toner at said elevated temperature.
 7. A method according toclaim 1 wherein at least said first liquid toner comprises a firstplasticizer for said polymer particles, said first plasticizer beingadditional to or different from an amount or type from any plasticizerthat may be present in said at least one additional liquid toner.
 8. Amethod according to claim 7 wherein said first plasticizer comprises DiButyl phtalate.
 9. A method according to claim 7 wherein said firstplasticizer comprises Acetyl tri-ethyl citrate.
 10. A method accordingto claim 7 wherein said first plasticizer comprises Acetyl tri-butylcitrate.
 11. A method according to claim 1 wherein said pigmentedpolymer particles in said first liquid toner comprise a differentpolymer or mixture of polymers than the pigmented polymer particles insaid at least one additional toner.
 12. A method according to claim 11wherein one of the polymers is an ethylene acid/methacrylic acidcopolymer.
 13. A method according claim 11 wherein one of the polymersis an Acid-Modified Ethylene Acrylate.
 14. A method according to claim11 wherein one of the polymers is an ethylene acrylic acid copolymer.15. A method according to claim 1 wherein the pigmented polymerparticles in the first liquid toner and at least one additional tonerare formed in a process in which the polymer of the particles is heatedwith and plasticized by a liquid, some of which remains solvated by thepolymer after cooling the particles and wherein the proportionate amountor composition of said remaining solvated liquid is different for theparticles in the first and at least one additional toner.
 16. A methodaccording to claim 15 wherein said proportionate amount is different.17. A method according to claim 16 wherein the proportion by weight ofliquid in the first toner is over 30% by weight of polymer.
 18. A methodaccording to claim 16 wherein the proportion by weight of liquid in thefirst toner is over 35% by weight of polymer.
 19. A method according toclaim 16 wherein the proportion by weight of liquid in the at least oneadditional toner is less than 30% by weight of polymer.
 20. A methodaccording to claim 16 wherein the proportion by weight of liquid in theat least one additional toner is less than 25%.
 21. A method accordingto claim 15 wherein the composition of the remaining solvated liquid isdifferent in said first liquid toner than the one additional toner. 22.A method according to claim 21 wherein the liquid solvated of the firsttoner comprises liquid having an evaporation time compared toDiethylether of more than
 150. 23. A method according to claim 21wherein the liquid solvated in the first toner comprises liquid havingan evaporation time compared to Diethylether of more than
 250. 24. Amethod according to claim 21 wherein the liquid solvated in the at leastone additional toner comprises liquid having an evaporation ratecompared to BuAc of at least
 4. 25. A method according to claim 1wherein said at least one carrier liquid used in said first liquid tonerand at least one additional toner is different or comprises a mixture ofdifferent carrier liquids or a mixture of the same carrier liquids indifferent proportions.
 26. A method according to claim 1 wherein atleast one of the toners comprises a charged toner particle.
 27. A methodaccording to claim 26 wherein forming an image comprises: forming alatent electrostatic image on an image forming surface; and contactingthe image with a liquid toner to form a visible image.
 28. A methodaccording to claim 1 wherein the liquid toners comprise at least cyan,magenta and yellow toners.
 29. A method according to claim 28 whereinthe liquid toners comprise a black toner.
 30. A method according toclaim 28 wherein the liquid toners comprise one or more of violet,orange and green toners.